This invention relates to retorting processes for recovering product hydrocarbons from oil shale and other hydrocarbon-bearing solids. More specifically, this invention relates to the cooling and depressurizing of retorted oil shale particles removed from an oil shale retort operated at superatmospheric pressure without loss of retort product gases and without substantial emissions of noxious gases.
Many methods for recovering oil from oil shale have been proposed, nearly all of which utilize some method of pyrolytic eduction commonly known as retorting. It is known to retort oil shale by a technique of contacting upflowing oil-bearing solids with downflowing gases in a vertical retort, and one such technique is disclosed in U.S. Pat. No. 3,361,644. To educe product vapors, the upward-moving bed of shale particles exchanges heat with a downflowing, hydrocarbonaceous and oxygen-free eduction gas of high specific heat introduced into the top of the retort at about 950.degree. to 1200.degree. F. In the upper portion of the retort, the hot eduction gas educes hydrogen and hydrocarbonaceous vapors from the shale and, in the lower portion, preheats the ascending bed of particles to retorting temperatures. As preheating continues, the eduction gas steadily drops in temperature, condensing high boiling hydrocarbonaceous vapors into a raw shale oil product while leaving a product gas of relatively high BTU content. The shale oil and product gas are then separated, and a portion of the product gas, after being heated, is recycled to the top of the retort as the eduction gas.
To minimize the volume of the recycle gas required, upflow retorting is usually conducted with superatmospheric pressures, with the pressure in the upper regions of the retort often being between 10 and 30 p.s.i.g. However, means must be provided for introducing and recovering granular shale from the superatmospheric retorting zone without allowing valuable product and recycle gases to depressure. Conventional methods for achieving these objectives use elaborate lock vessels, valves, star feeders, or slide valves, which tend to wear rapidly and produce excessive fines through abrading the shale. Alternatively liquid sealing devices, as in U.S. Pat. No. 4,004,982, have been employed, which operate by moving shale particles through a standing head of oil or water, thereby creating a positive back pressure to forestall escape of retort gases. Liquid seals effectively contain retort gases but leave the shale saturated. Saturated shale causes operating problems resulting from weakened particle strength.
Conventional methods for cooling the retorted oil shale particles have also proven to be less than satisfactory. Such methods usually involve quenching the particles with water, a technique which leaves the shale undesirably liquidsaturated and consumes large quantities of water.
While the aforementioned features have met with some success, the need exists for further developments in shale retorting processes. For example, the need exists for a process by which retorted shale can be removed from a retort operating at superatmospheric pressure without loss of retort gases and be delivered in a cooled, dry condition suitable for disposal as landfill without excessive use of water or unacceptable pollution to the environment.
Accordingly, the principal object of this invention is to provide an easily installable apparatus of moderate height and a process for its use in removing retorted shale particles of relatively high sulfur content from a super-atmospheric oil shale retort while preventing loss of gases therefrom, partially cooling the shale, and avoiding unacceptable levels of environmental pollution.
It is an additional object to provide an alternative embodiment of this invention for use in localities where emissions of environmental pollutants are unregulated or for use with retorted particles of relatively low sulfur content.
It is another object of the invention to provide an apparatus and process for depressurizing and cooling retorted shale particles without using excessive quantities of water.
It is a further object of this invention to provide an apparatus and process for recovering retorted shale particles from an oil shale retort in an essentially dry condition.